1. Field of the Invention
The present invention relates to the packaging of material for delivery, for example in gene therapy and other situations.
2. Description of the Related Art
Gene transfer, as a means to effect gene therapy, is becoming increasingly important. Numerous studies have been carried out that seek to harness the inherent ability of viruses to infect eukaryotic cells in order to introduce a selected gene into a suitable recipient host (as reviewed: Anderson, 1992; Morgan and Anderson, 1993; Mulligan, 1993). Adenoviruses have proved particularly attractive for this purpose in that their genome can be manipulated to incorporate up to 8 kbp of foreign DNA and, unlike retroviral vectors, transduced genes can be expressed in non-dividing cells. One particular handicap shared by all the present virus vectors, however, is that they introduce unwanted viral genetic information alongside the gene of interest into the recipient host. The disadvantages of this unwanted viral material remain to be determined fully, but there is a great need for means to carry out improved genetic transfer without introduction of unwanted viral genes into target cells.
Physical, non-viral gene transfer methods such a chemical and mechanical techniques and membrane fusion-mediated transfer via liposomes have been used (Morgan and Anderson, 1993). However, the efficiency of transfer, in terms of expression of the genetic material transferred, is low. In other words, these methods are inefficient at transferring genetic material into cells in a stable manner so that the material is biologically functional.
The empty capsids of papovaviruses such as the mouse polyoma virus have received attention as possible vectors for gene transfer.
Barr et al, 1979, first described the use of polyoma empty when polyoma DNA and purified empty capsids were incubated in a cell-free system. The DNA of the new particle was protected from the action of pancreatic DNase. Slilaty and Aposhian, 1983, describe the use of those reconstituted particles for transferring a transforming polyoma DNA fragment to rat FIII cells. The empty capsids and reconstituted particles consist of all three of the polyoma capsid antigens VP1, VP2 and VP3 and there is no suggestion that pseudocapsids consisting of only the major capsid antigen VP1, could be used in genetic transfer.
Montross et al, 1991, described only the major capsid antigen, the cloning of the polyoma virus VP1 gene and its expression in insect cells. Self-assembly of empty pseudocapsids consisting of VP1 is disclosed, and pseudocapsids are said not to contain DNA. It is also reported that DNA inhibits the in vitro assembly of VP1 into empty pseudocapsids, which suggests that said pseudocapsids could not be used to package exogenous DNA for transfer to host cells. The results of Sandig et al, 1993, showed that empty capsids incorporating exogenous DNA could transfer DNA in a biologically functional manner to host cells only if the particles consisted of all three polyoma capsid antigens VP1, VP2 and VP3. Pseudocapsids consisting of VP1 were said to be unable to transfer to exogenous DNA so that it could be expressed in the host cells. We know that this was probably because Ca.sup.2+ ions were not included in the medium in which the pseudocapsids were prepared. Haynes et al (1993) J. Virol., 67, 2486-2495) discuss the effect of calcium ions on empty VP1 pseudocapsid assembly. Hagensee et al (1993) J. Virol., 67, 315-322 disclosed the production of L1 and L1/L2 human papillomavirus capsids, but did not suggest their use to carry exogenous material.